Weighing apparatus

ABSTRACT

Weighing apparatus incorporated in a vehicle to be responsive to the load on the vehicle&#39;&#39;s axle(s) and to be used when the vehicle is in motion, which comprises mechanical low pass filtering means to attenuate sudden variations of the relative displacement between the vehicle&#39;&#39;s load carrying structure and axle(s) at least when the moving vehicle is heavily laden so that only the average value of this varying relative displacement is utilized in giving an indication of the load carried by said structure. The mechanical low pass filtering means comprises high rate spring means and mechanical damping means that have two closely spaced generally concentric cylindrical surfaces defining an annular gap which contains a silicone substance in fluid or compound form.

United States Patent Barrett 1541 WEIGHING APPARATUS [72] Inventor:Edward George Barrett, Witney, England Smiths Industries Limited,London, England [22] Filed: July 15,1970

[21] Appl,No.: 54,940

[73] Assignee:

[52] US. Cl ..177/l37, 177/210, 338/145 [51} Int. Cl. ..G01g 19/08, GOlg3/14 [58] FieldofSearch "177/136,137,138,210,184, 177/187; 338/145 [56]References Cited UNITED STATES PATENTS 3,092,818 6/1963 Potschka..l77/137 X 3,109,505 11/1963 Davis et al.. ..177/137 3,142,349 7/1964Blodgett ..177/210 X 3,151,692 10/1964 Dysart ..l77/l38 3,167,142 l/1965Meneely. ...177/l37 3,314,491 4/1967 Nelson ..177/138 [451 May 9,1972

Primary Examiner-Richard B. Wilkinson Assistant Examiner-George H.Miller, Jr.

Attorney-William D. Hall, Elliott l. Pollock, Fred C. Philpitt, GeorgeVande Sande, Charles F. Steininger and Robert R. Priddy [57] ABSTRACTWeighing apparatus incorporated in a vehicle to be responsive to theload on the vehicles axle(s) and to be used when the vehicle is inmotion, which comprises mechanical low pass filtering means to attenuatesudden variations of the relative displacement between the vehicle'sload carrying structure and axle(s) at least when the moving vehicle isheavily laden so that only the average value of this varying relativedisplacement is utilized in giving an indication of the load carried bysaid structure.

The mechanical low pass filtering means comprises high rate spring meansand mechanical damping means that have two closely spaced generallyconcentric cylindrical surfaces defining an annular gap which contains asilicone substance in fluid or compound form.

11 Claims, 4 Drawing Figures PATENTEDMAY 9:972 3,661,221

sum 1 UP 3 5 Tm: e -h/ WEIGHING APPARATUS CROSS REFERENCE TO RELATEDAPPLICATION The subject matter of this application is related to that ofBishop U.S. Pat. application Ser. No. 54,939, filed July 15, 1970, forWeighing Apparatus, and assigned to the same assignee as the instantapplication.

BACKGROUND OF THE INVENTION This invention relates to weighing apparatusand in particular to weighing apparatus of the kind adapted or intendedto be incorporated in a vehicle so as to be responsive to variations inthe load carried by the vehicle.

One type of apparatus of this kind, comprises an electrical indicator(preferably having a pointer co-operating with a scale) and a sensorcomprising two relatively movable elements (for example a contactelement arranged for wiping engagement of an electrical resistanceelement to vary the effective electrical resistance of the latter) whoserelative movement (hereinafter referred to as the induced relativemovement) produces a varying electric signal and is directly related tothe relative movement between the load-carrying structure of the vehicleand the road. Generally speaking the relative movement between theload-carrying structure and the road is equivalent to changes in theposition of the load-carrying structure relative to the road wheelsand/or to the axles of the vehicle, the axles supporting theload-carrying structure through springs whose vertical deflections arerelated to the total vertical forces acting on the springs.

Prior proposals for this type of apparatus (see for example US Pats. No.3,109,505; No. 1,147,127; No. 1,621,093; No. 3,167,142; and UK. Pat. No.1,018,510) have apparently assumed that the vertical deflections of thesprings are at all times directly related to the total load, i.e., tothe weight of the load-carrying structure plus the load (if any) carriedthereby. The applicant herein has now realized that, at least asconcerns certain forms of spring, in particular leaf-springs, thisfundamental assumption does not take into consideration the temporaryindeterminancy of the settling-position of the springs when the vehicleis stationary, which indeterminancy is believed attributable to theindeterminate variations in striction or friction, in particular betweenthe leaves of leaf springs, and that therefore the indications of loadgiven by the indicators of these prior proposals would be indeterminateand usually inaccurate when obtained with the vehicle stationary.

It will be readily apparent that a single electrical indicator can beused, with suitable circuit switching arrangements, for a plurality ofsensors that are each responsive to a proportion of the total verticalforces (hereinafter referred to as the pro portional forces) acting onthe springs, the average value of these proportional forces, which arenot constant when the vehicle is in motion, being directly related tothe proportion of the total load (hereinafter referred to as theproportional load") producing them. Therefore as used hereinafter, theterm primary relative movement is intended to mean the effectiveproportion of the relative movement between the loadcarrying structureand the road that produces the induced relative movement between the twoelements of one particular sensor.

SUMMARY OF THE INVENTION It is a primary object of this invention toprovide a durable and compact transducer mechanism for vehicle weighingapparatus of the aforesaid kind.

According to this invention there is provided for weighing I apparatusto be incorporated in a vehicle having an axle strucsociation with saidaxle structure; wherein said transducer mechanism comprises:

a. an input member,

b. means mounting said input member for angular movement,

c. an operating member to angularly move said input member at least whensaid relative movement exceeds a predetermined value,

d. a rotation member having a first cylindrical surface and an outersurface,

e. high rate spring means interconnecting said input member and saidrotation member and to transmit angu lar movement of said input memberto said rotation member,

f. a support member for said rotation member and having a secondcylindrical surface generally concentric with and slightly radiallyspaced from said first cylindrical surface to provide an annular gaptherebetween.

g. a silicone substance in said annular gap to damp relative movementbetween aid rotation member and said support member,

h. an electrical resistance element coiled about said outer surface,

i. a contact member, and

j. means mounting said contact element for wiping engagement of saidelectrical resistance element.

Other features of the present invention will be apparent from theappended claims and from the exemplary embodiments now to be describedwith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic rear view of atruck-like vehicle incorporating a transducer mechanism according tothis invention;

FIG. 2 is a partly cross-sectioned view of the transducer mechanism ofFIG. 1 taken longitudinally of the vehicle.

FIG. 3 is a schematic perspective view of part of the transducermechanism of FIG. 2; and

FIG. 4 is a similar view to FIG. 2 showing part of another similartransducer mechanism according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, atruck-like vehicle 10 comprises a cab 11 disposed above the v'ehiclesfront wheels (not shown) and, rearwardly of the cab, a platform 12 andsupporting girders 13 extending longitudinally of the vehicle toconstitute a load carrying structure. The load carrying structure issupported at the rear by longitudinally directed leaf springs 14shackled to the vehicle's transversely extending rear axle 15 thatdrives the rear ground-engaging wheels 16 through a differential gearbox 17. The weighing apparatus comprises in the cab 11 an electricalindicator (not shown) having a moving-coil type of movement operating apointer that co-operates with a scale calibrated in units of weight orin percentages (e.g. 70 to l 10 percent) of a maximum desired safetylimit for the proportional load, and secured beneath the platform 12 anencased transducer mechanism 20 comprising a sensor and mechanical lowpass filtering means (to be described below). An input shaft 72 of themechanism 20 projects from the mechanisms casing and is fastened to oneend of a long lever 24 whose free end (as shown in full lines) is spacedvertically above the differential gear box 17 and is disposedsubstantially centrally between the wheels 16. In the arrangement shown,the casing is vertically above the rear axle 15 to one side thereof anda cable or chain 26 (represented by a broken line restrains the lever 24from coming into contact with the difl'erential gear box 17 until theproportional forces in the springs 14 exceed a predetermined value suchas to cause the primary relative movement to take up the verticalspacing between the levers free end and the top of the differential gearbox, this position of lever 24 being shown by broken lines. Since thelever 24 is long, large generally vertical displacements of its free endproduce corresponding but small angular displacements of the input shaft72.

As shown in FIGS. 2 and 3, the casing for the transducer mechanism(indicated by the reference numeral 70) is a cast housing having an endwall 74 in which bearings 73 support for rotation the input shaft 72.The end wall 74 has integral extensions by means of which the housing 70may be attached to the underside of platform 12. Within the housing 70 ahigh rate spiral spring 75 has its inner end 76 secured to the inner endof shaft 72 and its outer end 77 secured to an anchor post 78 (FIG. 3)extending longitudinally from the end 79 of a radially projecting arm 80that is integral with a generally circular plate 82. Plate 82 is securedby bolts or screws 81 to a generally cylindrical hollow drum 84 moldedof a suitable plastics material integrally with a projecting bead 85,and rotatably mounted upon a cylindrical support block 121 bolted to aback plate 90 itself secured by long bolts 89 to the housing end wall74. The bead 85 follows a helical path about the longitudinal axis ofdrum 84 (and therefore of input shaft 72) and has a small helix angle(i.e. a large pitch) preferably of the order of 20 of arc. Anelectrically resistive wire 122, constituting one element of a rheostatunit, is closely coiled about the surface of drum 84 so as to have alarge number of convolutions each having a small region overlying thebead 85, and has one end electrically connected to a conducting pin 91projecting through and insulatingly mounted in the back plate 90. Theother element of the rheostat is constituted by the base 95 of aU-shaped wire frame 92 whose leg ends 93 are coiled about a mountingpost 94 (having an encompassing sleeve of insulating material) mountedbetween the housing end wall 74 and the back plate 90. A coiledtorsional spring 96 surrounds the insulating mounting post 94 and hasone end hooked around the frame leg end 93 adjacent plate 82 and itsother end secured to a conducting pin 97 insulatingly projecting throughand secured to the back plate 90. Spring 96 thus serves both to urgebase 95 into constant abutment with the resistive wire regions overlyingbead 85, and also to electrically connect the base 95 to the conductingpin 97. It will be appreciated that the point or small area of contactbetween the frame base 95 and the resistive wire region overlying bead85 adopts a position longitudinally of cylindrical drum 84 that dependson the angular position of cylindrical drum 84. Since the bead 85 has asmall helix angle, a comparatively small change in the said angularposition causes a substantial change in the said longitudinal positionand consequently a substantial change in the effective resistance of therheostat.

Mechanical damping means to damp the angular movement of the cylindricaldrum 84 is provided by the presence of a silicone fluid or a siliconecompound (e.g. that sold in the United Kingdom by Midland SiliconesLimited under the Trade Mark RELEASIL 7) in an annular gap 120 betweenthe outer cylindrical surface of the support block 121 and the innercylindrical surface of the hollow drum 84. Conveniently the radialdimension of the gap 120 between these two cylindrical surfaces is ofthe order of six thousandths of an inch. Particularly where a siliconefluid is provided in the annular gap 120 between said two cylindricalsurfaces, the external surface of support block 121 is chamferedadjacent its annular end surface nearest plate 82 so as to provide areservoir space 123 for the silicone fluid, and if desired the end ofthe gap 120 adjacent the back plate 90 may be closed by an annularsleeve of polytetrafluoroethylene.

In use, when the proportion of the total load affecting the rear axle isincreased, the proportional forces thereby induced cause the rearleaf-springs 14 to be depressed so that the load-carrying structure 12moves nearer the rear axles and the rod 18. As indicated above,transmission of this primary relative movement to the transducermechanism is only commenced when the vertical separation between thedifferential gear box 17 and the free end of lever 24 is taken up. Thusan indication of the proportional load will only be obtained from theelectrical indicator (connected to the pins 91 and 97 in a circuitincluding a power supply of the vehicle) when the load is above somepredetennined value, preferably near the maximum desired safety limitfor this load. It will be appreciated that readings are taken of theelectrical indicator while the vehicle is in motion so that thetransmitted primary relative movement (equivalent to the verticaldepression of the leaf-springs), that produces the induced relativemovement between the two elements 95, 122 of the rheostat unit (whichinduced relative movement gives rise to indicator pointer deflection),is related to the proportional load. However, although the proportionalforces are continuously vary ing because the vehicle is in motion overbumps and pot-holes in the road, the average value of these varyingproportional forces is substantially equivalent to the proportional loadand it is this average value that causes the two elements 95, 122 of therheostat unit to take up relative positions which are substantiallynon-varying for a constant proportional load greater than thepredetermined value of proportional load.

In operation, once the vertical separation between the differential gearbox 17 and the free end of lever 24 is taken up, the primary relativemovement is equivalent to the vertical displacement of the levers freeend (which can move generally vertically because the pivotted lever 24is longer than this primary relative movement) and is thus proportionalto the angular displacement of the input shaft 72. In the steady state(i.e. the theoretical state when the proportional forces transmitted areconstant at their average value), the angular displacement of the inputshaft 72, and hence the inner end 76 of the high rate spiral spring 75,is equivalent to the angular displacement of the outer end 77 of thehigh rate spiral spring 75 and is transmitted to the plate 82 (servingas the aforesaid intermediate member) and to the drum 84 securedthereto. The small angular movements of the plate 82 and drum 84 aremechanically clamped by the silicone substance in the annular gapwhereby under steady-state conditions, the plate 82 and drum 84 take upan angular position directly proportional to the primary relativemovement. Since, as explained above, small changes in the angularposition of drum 84 result in large changes in the effective resistanceof the rheostat unit, the electric indicator connected in an electricalcircuit with this effective resistance through conducting pins 91 and 97may have a high ratio of scale division to unit of proportional load.

In an alternative arrangement, the cable or chain 26 may be omitted soas to enable the free end of lever 24 to continu ously abut the top ofthe differential gear box 17 (i.e. take up the position shown in FIG. 1by broken lines). In this case, the high rate spiral spring 75 may beassembled in a stressed condition and restrained from moving out of thiscondition when the primary relative movement is below said predeterminedvalue by the abutment 'of the end 119 of another radially projecting arm120' that is integral with plate 82 with stop means (not shown) that arecast integrally with housing 70. Thus the plate 82 will only be movedangularly when the primary relative movement exceeds a predeterminedvalue corresponding to a rotation of input shaft 72 sufiicient tounstress spiral spring 75.

It will be readily apparent that by arranging for the rheostat unit toonly produce an electrical signal to the indicator when the primaryrelative movement exceeds a predetermined value, the indicator need onlybe calibrated so that its minimum scale marking corresponds with theproportional load including said predetermined value of the primaryrelative movement.

In the modification schematically shown in FIG. 4, the plate 82 isomitted and the input shaft 72 is connected to the base 124 of acup-shaped, double-walled, cylindrical drum 125 (replacing theabove-described drum 84) through an elongate resilient flat strip 126serving as a high rate torsion spring and replacing the above-describedspiral spring 75. The support block 121 of FIG. 2 is replaced by acup-shaped member 127 secured to the back plate 90 that in thisarrangement forms the base of a cup-shaped housing replacing theabovedescribed housing 70. The cylindrical wall 128 of cup-shaped member127 is disposed between the inner and outer cylindrical walls 131 and132 of the drum 125 with a small annular gap 133, 134 between itself andeach of them respectively. The gap 133 (and if desired the gap 134 aswell) has a radial dimension of the order of 0.006 inches, and containsa silicone substance (i.e. either a silicone fluid or a siliconecompound, e.g., RELEASIL 7"). The center of the base 130 of cupshapedmember 127 is abutted by a nipple 135 of the drum 125 to provide apivotal andaxially stationary mounting for the drum. As before, the drum125 is molded of a suitable plastics material integrally with aprojecting helical bead (such as the bead 85 of FIG. 3) on the externalsurface of its wall 132 and is encompassed by the coiled electricallyresistive wire 122 constituting one element of the rheostat. If desired,a reservoir space 123 may be provided and a cylindrical sleeve 136 ofpolytetrafluoroethylene may seal the open end of annular gap 134. Inoperation of this arrangement, the proportion of the primary relativemovement causing input shaft 72 to rotate acts through the high ratetorsion spring 126 upon the drum 125 (which serves simultaneously as theaforesaid intermediate member and one component of the mechanicaldamping means) whose angular displacement is damped by the siliconesubstance.

It will be appreciated that an alternative disposition to that shown inFIG. 1 for the above-described transducer mechanism 20 may be achievedby securing the casing or housing thereof to the underside of platform12 centrally of the road wheels 16 above the differential gear box 17and by replacing the long lever 24 by a vertical rod having a rack atits upper end that is in mesh with a pinion on the input shaft 72. Thefree lower end of this rod may be vertically spaced from he differentialgear box 17 for abutment therewith only when the primary relativemovement exceeds said predetermined value, or may be in continuousabutment therewith with the spring means 75 or 126 in the housing beingpre-stressed.

It will be apparent that the transducer mechanism may be alternativelymounted on the axle or a part movable therewith with the free end of thelever or rod disposed for contact by the underside of the platform or apart movable therewith, that is to say the above described arrangementsmay be inverted.

What is claimed is:

1. For weighing apparatus to be incorporated in a vehicle having an axlestructure, ground engaging wheels mounted on said axle structure,springs acting on said axle structure, and a load carrying structuresupported by said springs for relative movement with respect to ground,and to be utilized when the vehicle is in motion, a transducer mechanismand means for mounting said transducer mechanism to one of saidstructures in vertical association with said axle structure; whereinsaid transducer mechanism comprises:

a. an input member,

b. means mounting said input member for angular movement,

c. an operating member to angularly move said input member at least whensaid relative movement exceeds a predetermined value,

d. a rotation member having a first cylindrical surface and an outersurface,

high rate spring means interconnecting said input member and saidrotation member and to transmit angular movement of said input member tosaid rotation member,

f. a support member for said rotation member and having a secondcylindrical surface generally concentric with and slightly radiallyspaced from said first cylindrical surface to provide an annular gapthere-between,

g. a silicone substance in said annular gap to damp relative movementbetween said rotation member and said support member, h. an electricalresistance element coiled about said outer surface,

i. a contact element, and j. means mounting said contact element forwiping engagement of said electrical resistance element. I A transducermechanism according to claim 1, wherein said silicone substance is asilicone compound.

3. A transducer mechanism according to claim 1, herein said high ratespring means comprises a spiral spring.

4. A transducer mechanism according to claim 1, wherein said high ratespring means comprises a flat strip torsion spring.

5. A transducer mechanism according to claim 1, wherein said outersurface is generally cylindrical and is provided externally with a ribthat follows a helical path of small helix angle about an axis of thegenerally cylindrical outer surface; and wherein said contact elementcomprises an elongate portion extending longitudinally of said generallycylindrical outer surface in wiping contact with said electricalresistance element above said rib.

6. A transducer mechanism according to claim 5, wherein said small helixangle is of the order of 20 of arc.

7. A transducer mechanism according to claim 1, wherein said rotationmember comprises a generally annular wall having an internal surface andan external surface, said external surface constituting the aforesaidouter surface.

8. A transducer mechanism according to claim 7, wherein said internalsurface constitutes the aforesaid first cylindrical surface.

9. A transducer mechanism according to claim 7, wherein said rotationmember comprises another generally annular wall disposed concentricallywithin and in radially spaced relation to the first-mentioned annularwall and having an external surface facing the internal surface of thefirst-mentioned annular wall; and wherein said support member comprisesan annular wall having an external surface and an internal surface thatconstitutes the aforesaid second cylindrical surface, said annular wallof the support member being disposed generally concentrically betweenthe annular walls of said rotation member.

10. For weighing apparatus to be incorporated in a vehicle having anaxle structure, ground engaging wheels mounted on said axle structure,springs acting on said axle structure, and a load-carrying structuresupported by said springs for relative movement with respect to ground,and to be utilized when the vehicle is in motion, an electricaltransducer to respond to movement between said two structures inaccordance with weight imposed on said load-carrying structure,comprising a first member having an outwardly-facing cylindricalsurface; a second member having an inwardly-facing cylindrical surfaceof larger diameter than said outwardly-facing cylindrical surface; meansfor coupling the two members to the said two structures respectively forangular displacement relative to one another in accordance with saidmovement, said coupling means including means mounting the two memberswith the said surfaces co-axial with one another to define an annulargap between the two members; damping means comprising a viscoussubstance in said gap to damp said relative angular displacement betweenthe two members; and an electrical pickoff for providing a measure ofsaid weight, said pick-off being responsive to said relative angulardisplacement between the two members to provide an electrical signal inaccordance with said relative angular displacement.

11. An electrical transducer according to claim 10, wherein saidelectrical pick-off comprises a resistance element carried with one ofsaid members, and a contact element for establishing electricalconnection with a point of said resistance element, the particular pointat which contact is made being dependent on the relative positions ofsaid resistance and contact elements; and wherein there is providedmeans mounting said contact element with respect to the other of saidmembers to make contact with said resistance element at a location whoseposition is dependent on said angular displacement.

* 1 i i I

1. For weighing apparatus to be incorporated in a vehicle having an axlestructure, ground engaging wheels mounted on said axle structure,springs acting on said axle structure, and a load carrying structuresupported by said springs for relative movement with respect to ground,and to be utilized when the vehicle is in motion, a transducer mechanismand means for mounting said transducer mechanism to one of saidstructures in vertical association with said axle structure; whereinsaid transducer mechanism comprises: a. an input member, b. meansmounting said input member for angular movement, c. an operating memberto angularly move said input member at least when said relative movementexceeds a predetermined value, d. a rotation member having a firstcylindrical surface and an outer surface, e. high rate spring meansinterconnecting said input member and said rotation member and totransmit angular movement of said input member to said rotation member,f. a support member for said rotation member and having a secondcylindrical surface generally concentric with and slightly radiallyspaced from said first cylindrical surface to provide an annular gapthere-between, g. a silicone substance in said annular gap to damprelative movement between said rotation member and said support member,h. an electrical resistance element coiled about said outer surface, i.a contact element, and j. means mounting said contact element for wipingengagement of said electrical resistance element.
 2. A transducermechanism according to claim 1, wherein said silicone substance is asilicone compound.
 3. A transducer mechanism according to claim 1,herein said high rate spring means comprises a spiral spring.
 4. Atransducer mechanism according to claim 1, wherein said high rate springmeans comprises a flat strip torsion spring.
 5. A transducer mechanismaccording to claim 1, wherein said outer surface is generallycylindrical and is provided externally with a rib that follows a helicalpath of small helix angle about an axis of the generally cylindricalouter surface; and wherein said contact element comprises an elongateportion extending longitudinally of said generally cylindrical outersurface in wiping contact with said electrical resistance element abovesaid rib.
 6. A transducer mechanism according to claim 5, wherein saidsmall helix angle is of the order of 20* of arc.
 7. A transducermechanism according to claim 1, wherein said rotation member comprises agenerally annular wall having an internal surface and an externalsurface, said external surface constituting the aforesaid outer surface.8. A transducer mechanism according to claim 7, wherein said internalsurface constitutes the aforesaid first cylindrical surface.
 9. Atransducer mechanism according to claim 7, wherein said rotation membercomprises another generally annular wall disposed concentrically withinand in radially spaced relation to the first-mentioned annular wall andhaving an external surface facing the internal surface of thefirst-mentioned annular wall; and wherein said support member comprisesan annular wall having an external surface and an internal surface thatconstitutes the aforesaid second cylindrical surface, said annular wallof the support member being disposed generally concentrically betweenthe annular walls of said rotation member.
 10. For weighing apparatus tobe incorporated in a vehicle having an axle structure, ground engagingwheels mounted on said axle structure, springs acting on said axlestructure, and a load-carrying structure supported by said springs forrelative movement with respect to ground, and to be utilized when thevehicle is in motion, an electrical transducer to respond to movementbetween said two structures in accordance with weight imposed on saidload-carrying structure, comprising a first member having anoutwardly-facing cylindrical surface; a second member having aninwardly-facing cylindrical surface of larger diameter than saidoutwardly-facing cylindrical surface; means for coupling the two membersto the said two structures respectively for angular displacementrelative to one another in accordance with said movement, said couplingmeans including means mounting the two members with the said surfacesco-axial with one another to define an annular gap between the twomembers; damping means comprising a viscous substance in said gap todamp said relative angular displacement between the two members; and anelectrical pick-off for providing a measure of said weight, saidpick-off being responsive to said relative angular displacement betweenthe two members to provide an electrical signal in accordance with saidrelative angular displacement.
 11. An electrical transducer according toclaim 10, wherein said electrical pick-off comprises a resistanceelement carried with one of said members, and a contact element forestablishing electrical connection with a point of said resistanceelement, the particular point at which contact is made being dependenton the relative positions of said resistance and contact elements; andwherein there is provided means mounting said contact element withrespect to the other of said members to make contact with saidresistance element at a location whose position is dependent on saidangular displacement.